Multi-axle vehicles used for carrying large loads of cargo or passengers often have at least one tandem axle, which is a group of two or more axles situated close together. Such tandem axles are used to provide greater weight capacity than a single axle. When a multi-axle vehicle is being driven, the vehicle is likely to encounter rough road, bumps, and the like that cause one axle of a tandem axle to move to a higher or lower level than its adjacent axle. Moreover, this axle movement may be more pronounced on one side of each axle.
With no suspension system, the road forces are transferred directly to the truck frame, causing a rough, and oftentimes unsafe, ride. Accordingly, in view of the greater weight capacity, additional consideration is given to suspension systems for multi-axle vehicles to provide safer transport for the driver, any passengers, and/or any cargo. As will be discussed more fully below, as it relates to “PRIOR ART” drawings FIG. 1 and FIG. 2, a conventional suspension system for a tandem axle vehicle has a pair of springs, most often a pair of leaf springs, and an equalizer between adjacent axles of a tandem axle.
Each leaf spring used in a suspension system for a tandem axle is typically mounted on one end to the vehicle frame through a hanger assembly. The other end of a leaf spring cooperates with the equalizer. The center portion of the leaf spring is mounted to one end of an axle, for example with a U-bolt.
Equalizers are used to help balance the load between adjacent axles of a tandem axle. An equalizer is pivotably mounted to the vehicle frame between adjacent axles. The equalizer is also adapted to directly or indirectly receive one end of a forward spring and one end of a rearward spring.
Leaf springs and equalizers cooperate to stabilize a vehicle on smooth roads, as well as over rough terrain. The suspension system cushions the chassis and enables the driver to better steer the vehicle under a variety of conditions. Ideally, a suspension system provides a smooth ride when both loaded and unloaded. However, when a spring is compressed in reaction to dissimilar weights/heights between axles or across an axle, the spring will eventually rebound causing the axle or end of that axle to kick back with force. Oscillation is a term of the art describing rhythmic or irregular vibrations in a suspension system. These oscillations are most prevalent when the vehicle is not loaded because the springs are designed to handle heavy loads and may not compress sufficiently with light weights. As a result, the vehicle will often resonate between tires as reactions to bumps are transferred back and forth between axles. Leaf springs are therefore often provided in a so-called spring pack to help dampen these oscillations through interleaf friction.
However, repeated oscillations can have adverse effects on tire wear, shimmying of the front wheels and/or spring breakage. Accordingly, there is a need for improving suspension systems and their components to balance loads on tandem axles, as well as to reduce oscillations.
To that end, U.S. Pat. No. 7,918,478B2 (Fenton) and its related patents (U.S. Pat. No. 7,296,821B2 (Fenton), U.S. Pat. No. 7,753,399B2 (Fenton et al) and U.S. Pat. No. 7,854,445B2 (Fenton et al)) describe an equalizer with internal elastomeric shock absorbing components of various shapes. The elastomeric pieces of the various embodiments in the Fenton and Fenton et al patents are designed to dampen or absorb harsh shocks or vibrations from the springs to provide a softer ride for the vehicle. As an equalizer arm moves upwardly, an internal shock plate is moved against the internal elastomeric shock absorber, causing deformation of the elastomeric shock absorber. According to the Fenton and Fenton et al patents, this deformation of the elastomeric shock absorber absorbs or dampens the harsh shocks or vibrations coming from the rear end of the leaf spring, which would otherwise be transferred through the equalizer to the center frame hanger and, thus, to the frame of the trailer.
Similarly, U.S. Pat. No. 7,753,400B2 (Dunlap et al) describes an equalizer with an integrated polymeric spring member. The integrated polymeric spring member is disposed between two arms of the equalizer, the arms in pivoting relationship to one another. Likewise, U.S. Pat. No. 3,504,929 (King) also shows an equalizer having pivoting arms. In this case, the arms have a spring disposed therebetween.
U.S. Pat. No. 5,024,462 (Assh) describes a combined air and leaf spring suspension for vehicles. The suspension has a load and shock transmitting lever at one end of a leaf spring. The other end of the lever has a pneumatic balloon solid with the end of the lever and the vehicle body. The pneumatic balloon has a hollow body with resilient sidewalls. A resilient damper element is disposed within the hollow body and is solid with the load and shock transmitting lever. The damper element projects upwardly and stops short of the vehicle body to define a stroke of a predetermined length.
U.S. Pat. No. 6,015,158 (Overby) relates to a front axle suspension having an equalizer assembly with a lever arm. The midpoint of the lever is connected to the rear end of a leaf spring and to one end of a shock absorber. A rubber or air spring is mounted on the forward end of the equalizer lever. When the wheel of the front axle hits a pot hole, the leaf spring drops down, causing the equalizer lever to move downwardly relative to the frame. The shock absorber dampens the downward movement of the midpoint of the lever. At the same time, movement of the lever causes the rubber or air spring to elongate. Once the wheel is out of the pot hole, the forward end of the lever moves up and compresses the rubber or air spring.
Each of these solutions to suspension system problems has a specific equalizer design and requires the specialized equalizer to be installed with the suspension system. None of these solutions can be readily combined with standard or other custom equalizer devices either to be sold or purchased together or as a kit for retrofitting an installed or separately purchased equalizer.
There is a need for a device that can be adapted to a variety of equalizer designs for damping shocks applied to axles of tandem axles. There is also a need for a kit that can be used to retrofit a conventional or other commercially available equalizer designs.